Drum series printer with stop pawl engaged by a snap-over spring

ABSTRACT

A printer is disclosed having type members carrying type characters, the members being yieldably advanced past a printing point and arrested by electromagnetically actuated pawls which are yieldably maintained in both retracted positions and arresting positions by snap-over springs. Abutments on the type members engage the pawls when the type members are in home positions to prevent accidental movement of the pawls to arresting positions. The electromagnetically operable means comprises pairs of side-by-side magnet modules in which each module is effective to retain the parts of an adjacent module in place.

United States Patent Weinkle [54] DRUM SERIES PRINTER WITH STOP PAWL ENGAGED BY A SNAP-OVER SPRING [72] Inventor: David Weinkle, Sierra Madre, Calif.

[73] Assignee: Addmaster Corporation, San Gabriel,

Calif.

[22] Filed: July 6, 1970 [21] Appl. No.: 52,264

[52] US. Cl ..10l/99, 101/95 [51] Int. Cl. ..B4lj 7/34, B413 7/48 [58] FieldofSearch ..l01/91,92, 93 C, 95, 96, 99,

[56] References Cited UNITED STATES PATENTS 3,468,245 9/1969 Ritzerfeld 101/91 3,101,927 8/1963 Gray .188/82.7 X 3,379,075 4/1968 Harrison 101/95 X 2,850,348 9/1958 Rueger 101/92 X [151 3,664,259 [4 1 May 23, 1972 3,501,130 3/1970 Utermohle... ..l88/82.3 X 2,873,848 2/1959 Steinmetz ....l88/82.4 X 3,002,448 10/1961 Pearson 101/92 X 2,879,712 3/1959 Mark lOl/95 3,482,512 12/1969 Jung..... ..lO1/1l0 Primary ExaminerWilliam B. Penn Assistant Examiner-E. M. Coven Attorney-Fred N. Schwend [57] ABSTRACT 13 Claims, 7 Drawing Figures Patented May 23, 1972 3,664,259

2 SheetS Sheet l INVENTOR DA v/0 W'I/NKL 1:

BYALZM/ DRUM SERIES PRINTER WITH STOP PAWL ENGAGED BY A SNAP-OVER SPRING BACKGROUND OF THE INVENTION This invention relates to data printers and has particular reference to printers of the cyclically operable type, embodying type members carrying a set or font of type characters thereon. Such members are yieldably advanced past a printing line and are arrested at different times by electromagnetically operated arresting means so as to position selected ones of the type characters at the printing line. Later in the cycle, and after all of the type members have been differentially posi tioned, printing hammers or the like are actuated to imprint the selected type characters against a record medium.

Printers of the above type generally incorporate type members having stop teeth adapted to be engaged by electromagnetically operated pawls. Such pawls are spring held out of tooth engaging position and are actuated at different time intervals depending upon the particular type character to be printed. Thereafter, the pawls are held in tooth engaging pulses positions until after the printing impression is made whereupon they are released to be returned to disengaging positions under the urge of their springs.

Although printers of the above type operate satisfactorily, a steady current must be applied to the electromagnets to hold the pawls in tooth engaging positions until after the printing impression has been made. Also, the pawl retracting springs must be made strong enough to insure that the pawls are normally fully retracted. Thus, the electromagnets must be made of adequate size and sufficient current must be passed therethrough to insure that they will be adequately actuated against the full force of their springs and within the time alloted. Such timing is relatively critical.

Although larger size electromagnets and larger amounts of current may be used to insure reliable operation of the stop pawls against the action of their springs as well as friction and inertia forces a practical limitation, particularly in size, is dictated by the lateral spacing allowed when it is desired to maintain a certain minimum spacing between adjacent printed type characters. Also, larger size electromagnets and current carrying electrical equipment naturally increase the cost.

SUMMARY OF THE INVENTION The present invention overcomes the above problems by providing snap-over springs which are effective to hold the stop pawls in either tooth arresting or retracted positions. This construction enables the pawl springs to actually aid the electromagnets in actuating the pawls after the snap-over point is reached, thus reducing the electrical power required and permitting smaller size electromagnets to be used. Further, only pulses of short and invariable time duration are required rather than a steady holding current which otherwise would have to be maintained to hold the pawls in position against the action of their springs until the printing impression has been effected. This reduces heating of the magnetic coils and permits a greater latitude in selection of electrical controls. Positive retraction of the pawls is provided by the sector teeth which are arranged to cam the pawls past the snap-over point of their springs during return movement of the type members to their home positions.

A still further feature of the invention is the arrangement whereby the snap-over point is so positioned that the detenting action holding the springs in their retracted positions is less than the detenting action holding the pawls in tooth arresting positions. Thus, only a very light detenting spring force needs to be overcome by the electromagnets in moving the pawls. Although this might otherwise leave the pawls subject to being moved to tooth arresting positions due to jarring or vibratory forces resulting, for example, from handling the printer when in non-operating condition, means are provided to firmly hold the pawls in their retracted positions when the type members are in their normal home positions and to release them to the detenting force of their springs only when the type members are being moved from their home positions.

It therefore becomes the principle object of the present invention to provide a cyclically operable printer of the above type capable of relatively high speeds while enabling relatively small stop pawl actuating electromagnets and small currents to be used to differentially arrest the type members.

Another object is to provide a data printer of the above type in which only momentary electrical pulses are required to set the stop pawls in tooth arresting positions.

A further object is to positively hold the detent pawls out of tooth arresting positions during periods when the type members are in home positions.

BRIEF DESCRIPTION OF THE DRAWINGS The manner in which the above and other objects of the invention are accomplished will be readily understood on reference to the following specification, wherein:

FIG. 1 is a longitudinal sectional view through a data printer embodying a preferred form of the present invention.

FIG. 2 is a sectional plan view taken substantially along the line 22 ofFIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2.

FIG. 4 is an enlarged sectional plan view, with parts broken away, taken substantially along the line 4--4 of FIG. 1.

FIG. 5 is an enlarged sectional view, with parts broken away, taken along line 5-5 of FIG. 1.

FIG. 6 is a greatly enlarged fragmentary sectional view illustrating a stop pawl in tooth arresting position.

FIG. 7 is a sectional view, similar to FIG. 5 but illustrating the stop pawl in retracted position.

FIG. 8 is a fragmentary view, similar to FIG. 6 but illustrating a modified form of snap-over spring.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the printer disclosed therein comprises a plurality of plastic printing sectors arranged in side-by-side relation, one of which is shown at 11. The sectors are pivotally supported independently of each other on a support shaft 12. Each sector has a somewhat flexible arcuate type section 13 which is integrally connected to the main body thereof by end sections 14 and 15 of greater flexibility than that of the main part of the section 13. Printing type characters l6, ranging in value from zero to nine, are spaced along the length of each type section 13.

The print impressing means comprises a plurality of elongate type hammers 17 aligned with respective ones of the sec tors l1 and guided for endwise movement in a direction radially of the sectors by stationary guide members 18 and 20, the latter extending through elongate guide slots 21 and the hammers.

A paper tape 22 is guided for endwise movement between the lower ends of the hammers 17 and the sectors 11 by a channel formed by paper guide members 23 and 24. The tape is advanced endwise through the guide channel by a feed roller 25 against which the tape is pressed by a spring pressed ball 26. The tape passes over a printing ribbon 27, extending over the sectors 11 and is then deflected upwardly along a vertical portion 23a of the guide member 23 by a transparent tear-off member 28.

Leaf springs 30 connected to respective ones of hammers 17 are effective to impel the hammers downwardly during a midpoint in each printer cycle. Such springs are attached at 31 to a part of the machine frame and are normally held in their illustrated positions by a cam follower 131 pivoted at 32 and engaged by a three lobe cam 33 carried by a printer control shaft 34.

Means are provided for yieldably advancing the various sectors 11 in a clockwise direction from their illustrated home positions during the first half of a printer cycle until differentially arrested, as will be described presently, and after such advancement the shaft 34 will rotate clockwise permitting the cam follower 131 to drop off one of the lobes of cam 33 to permit the hammers to be impelled downwardly by springs 30 into printing contact with the paper tape. Thereafter, the following cam lobe will retract the hammers and thereafter the sectors 11 are returned counterclockwise to their home positions For this purpose, a bail rod 35 extends through openings 36 in the sectors 11 and engages shoulders 37 formed on yieldable tails 38 which are integral with the sectors. As disclosed in the detail in the co-pending U.S. patent application of J. G. Clary, Ser. No. 16,316, filed on Mar. 4, 1970 for DATA PRINTER and since matured into US. Pat. No. 3,621,777, issued on Nov. 23, 1971., the bail rod 35 is carried clockwise in an orbit about the sector support shaft 12 during the first part of the cycle to yieldably advance the sectors until the latter are differentially arrested. Thereafter, and before the print hammers are impelled downwardly, an aligner bar 39 is raised to engage in one of the series of notches 49 in each of the type sections 13. Finally, after the printing operation takes place, the bail rod 35 is returned counterclockwise, causing it to engage slightly yieldable fingers 40 to similarly return the sectors to their home positions.

For the purpose of differentially arresting the sectors to present selected type characters to a printing line located directly below the hammers 17, each sector has a set of teeth 41 thereon. Such teeth are spaced apart angular distances equal to the angular spacings of the type characters 16. Teeth 41 are engageable by stop pawls 42, there being one stop pawl for each sector. Pawls 42 are pivotally supported on a stationary rod 43 suitably supported at opposite ends by frame plates, one of which is shown at 44 (FIG. 2). The various stop pawls are guided for lateral movement by triangularly shaped flanges 45 formed on electromagnet modules generally indicated at 48. Such flanges 45 also laterally guide the lower ends ofthe sectors 11. The modules are located in side-by-side relation and are supported by the rod 43 and by a second rod 47. Suitable means (not shown) is provided to hold the modules laterally in engagement with each other.

The various modules 48 are arranged in pairs. The lefthand module of each pair comprises a rectangular plastic frame 50 having a central groove or cavity 51 therein which slideably supports a push rod or interponent 52 for endwise movement, the upper end of the rod engaging in a recess 53 in an associated stop pawl 42. The groove 51 is closed to slideably retain the push rod 52 by a tongue 54 (FIG. 4) formed on the frame 55 of the adjacent right-hand module of the same pair. Groove 51 opens into a second groove or cavity 56in which is loosely fitted the armature 57 of an electromagnet. The latter comprises a horseshoe shaped core 58 of magnetizable material and a coil 60. Coil 60 extends in an opening formed in the frame 50. A fulcrum tip 61 is formed on the frame 50 adjacent one end of the groove 56 to form a pivotal support for the armature. Groove 56 is also closed by the next adjacent frame 55 to slideably retain the armature.

The electromagnet is locked in place in the frame 50, and for this purpose, the return bend of the core 58 is fitted in an arcuate groove 62 formed in the frame 50, such groove being closed by the wall of the adjacent frame 55. The lower ends of the legs of the core 58 are fitted in notches 59 which are also closed by the adjacent frame 55 to prevent movement of the core.

Upon energization of the coil 60, the flux developed in core 58 will attract the armature 57 upwardly thereby causing the push rod 52 to rock the stop pawl 42 from its retracted position shown in FIG. 7 towards its tooth arresting position shown in FIG. 6.

The right-hand frame 55 (FIGS. 2, 3, 4 and of each pair of modules has a similar central groove 51 to guide a push rod 52 and a connected groove 63, similar to groove 56, to receive an armature 64 adapted to be actuated by an electromagnet comprising a core 65 and coil 66. The centers of the various grooves 51 are located in a common plane. The core 65 and coil 66 are similar to the core 58 and coil 60 earned by the frame 48 but are located on the side of the frame opposite those contained in frames 48, i.e. on the opposite side of the plane passing through the grooves 51.

In view of the alternate locations of the magnetic coils in adjacent ones of the frames 50 and 55 the coils may be made larger in diameter than the lateral spacings of the modules and pawls, as seen particularly in FIG. 4.

A toggle type detent spring 67 is provided to yieldably maintain each of the pawls in either its retracted position of FIG. 7 or its tooth arresting position of FIG. 6. Such spring is U- shaped and has outwardly extending feet which engage in V- shaped notches 68 and 70 formed in the pawl 42 and in the frame, i.e. 50, respectively. The spring is of thin highly resilient metal having a width less than the width of its respective pawl 42.

When a pawl 42 is in its retracted position (FIG. 7) a line c extending between the notches 68 and 70, and representing the line of force exerted by the spring 67 when a pawl is in its retracted position, extends at an angle a from the point of cross-over or snap-over of the spring, as represented by a line d. Such angle a is less than the angle b (FIG. 6) assumed when the tooth is in its tooth arresting position (FIG. 6). Preferrably, the angle a is just sufficient to hold the pawl in retracted position against normal vibration or jarring forces which may occur during clockwise advancement of these sectors by the bail rod 37. Thus, a minimum force is required by the associated electromagnet to overcome the detenting action of the spring 67 to advance the stop pawl 42 toward tooth anesting position. On the other hand, when the pawl crosses the cross-over point the spring 67 will aid the electromagnet in moving the pawl to its tooth arresting position and the angle b is preferrably such that when the pawl fully reaches such tooth arresting position the detenting force exerted by the spring is sufficient to prevent bounce-back of the pawl when it engages the sector 11.

It should be noted that each tooth 41 and pawl 42 have interengaging surfaces 71, the centers of which, when engaged as shown in FIG. 6, extend perpendicular to a line e passing between the pivotal axis of the pawls and the pivotal axis of the sectors 11 so that the tooth 41 engaging the pawl will tend to force the pawl further into tooth engagement.

Also, each tooth 41 has its tip surface 73 inclined at an angle fto a line 74 which is perpendicular to a radial line 75 passing through the pivot axis of the sector 11 so that the pawl may strike the tip of a proceeding tooth 41 and yet continue to advance to tooth arresting position as the sector advances. A pocket or tooth opening 76 is provided at the leading edge of each tooth whereby the pawl 42 may move into a detenting position with respect to the sector as the surfaces 71 engage.

As noted before, the spring 67 is effective to maintain the pawl in its tooth engaging position shown in FIG. 6 after the pulse applied to the corresponding coil, i.e. 60, has decayed. Now, upon return of the sectors 11 in a counterclockwise direction by the bail rod 35, a shoulder 77 on a preceeding tooth 41 engages an inclined surface 78 on the pawl to cam the latter toward its retracted position.

Thereafter, the inclined surface 73 further cams the pawl but at a slower rate of speed. Generally, the momentum of the pawl 42, in addition to the force exerted by the spring 67, should be sufficient to fully retract the pawl. However, if the pawl should not fully retract, a shoulder 80 of the sector will engage a shoulder 81 on the pawl as the former advances to its home position, thereby firmly retracting the pawl and holding it retracted until the next cycle. Thus, the pawl 42 will be prevented from being advanced to tooth arresting position due to inadvertment energization of the corresponding electromagnet or due to any jarring or vibrating forces which may be transmitted thereto when the printer is not operating.

A second set of teeth are formed on the sectors 11 to permit the stop pawl modules to be located in position to arrest different ones of said second set or to permit a second set (not shown) of such modules to be located in such position.

FIG. 8 illustrates a modified form of the invention in which its toggle springs are fonned of resilient wire. In this case, each spring 67a terminates in lateral extensions 75 and 76 which are fitted in bearing holes formed in the pawl 42 and associated frame.

I claim:

1. In a data printer having a printing impression means,

a type member having teeth thereon,

a plurality of type characters carried by said member,

cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means,

a stop pawl device having a part engageable with said teeth to arrest said member,

means for guiding said pawl device from a retracted position to an arresting position for arresting said type member in different positions to present different ones of said type characters to said impression means, and

means for moving said pawl device from said retracted position to said arresting position the combination with said pawl device of a snap-over spring engageable with said pawl device,

means supporting said spring to yieldably maintain said pawl device either in said retracted position or in said arresting position, and

means operable by said cyclically operable means for returning said pawl device to said retracted position and for maintaining said pawl device in said retracted position independently of said spring when said cyclically operable means is in said full cycle position.

2. The combination according to claim 1 comprising means for pivotally supporting said pawl device for movement between said arresting position and said retracted position,

the angle between said retracted position and an intermediate position representing the cross-over point of said snap-over spring being less that the angle between said arresting position and said intermediate position whereby said snap-over spring effects a greater detenting force against said pawl in said arresting position than in said retracted position.

3. The combination according to claim 1 comprising means for pivotally supporting said type member for movement about a first axis,

means for pivotally supporting said pawl device for movement about a second axis,

the engaging surfaces of each of said teeth and said device upon engagement extending perpendicular to a line passing between said axes whereby said surfaces will tend to drive said pawl device toward said member upon engagement of said surfaces.

4. The combination according to claim 1 comprising means operable by said cyclically operable means for returning said member to said initial position, said teeth being effective during return of said type member from a position in which said member is arrested by said pawl device to move said pawl device from said arresting position to said retracted position.

5. The combination according to claim 1 comprising means operable by said cyclically operable means for returning said member to said initial position, and

means comprising said member when in said initial position for holding said pawl device in said retracted position.

6. The combination according to claim 5 wherein said last;

mentioned means comprises an abutment on said member engageable with said pawl.

7. In a data printer having printing impression means, a plurality of type members arranged side-by-side, a plurality of type characters carried by said members, means for yieldably advancing said type members to carry said type characters past said impression means, stop pawls engageable with said type members whereby to arrest said members, and means for guiding said pawls from retracted positions to arresting positions for arresting respective ones of said type members in different positions to present different ones of said type characters to said impression means the combination with said pawls of electromagnetic modules arranged side-by-side,

each of said modules comprising a frame having first and second open guide cavities therein communicating with each other,

an electromagnet carried by said frame,

an interponent moveable in said first cavity and engageable with a said pawl,

an armature moveable in said second cavity and engageable with said interponent,

said armature being operable by said electromagnet to move said interponent to move said pawl from said retracted position to said arresting position, and

the frame of each of said modules except a end one closing the said cavities in a neighboring one of said frames.

8. The combination according to claim 7 comprising a third cavity in each of said frames for receiving a respective one of said electromagnets,

the frame of the neighboring said module closing said third cavity.

9. The combination according to claim 7 wherein the centers of said first cavities are located in a common plane, and

alternate ones of said electromagnets are located on opposite sides of said common plane.

10. The combination according to claim 7 wherein certain of the walls of said cavities guide the respective ones of said interponents and said armatures.

11. The combination according to claim 1 wherein said last mentioned means exerts a greater force against said pawl device than said spring.

12. In a data printer having a printing impression means,

a type member having teeth thereon,

a plurality of type characters carried by said member,

cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means,

a stop pawl device having a part engageable with said teeth to arrest said member,

means for guiding said pawl device from a retracted position to an an-estin position for arresting said type member in different positions to present different ones of said type characters to said impression means, and means for moving said pawl device from said retracted position to said arresting position,

the combination with said pawl device of spring means for yieldably maintaining said pawl device either in said retracted position or in said arresting position, and

means operable by said cyclically operable means for returning said pawl device to said retracted position and for maintaining said pawl device in said retracted position independently of said spring means when said cyclically operable means is in said full cycle position.

13. In a data printer having a printing impression means,

a type member having teeth thereon,

a plurality of type characters carried by said member,

cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means,

a stop pawl device having a part engageable with said teeth to arrest said member,

means for guiding said pawl device from a retracted position to an arresting position for arresting said type member in different positions to present different ones of said type characters to said impression means, and

means for moving said pawl device from said retracted position to said arresting position,

the combination with said pawl device of a snap-over spring engageable with said pawl device,

means supporting said spring to yieldably maintain said pawl device either in said retracted position or in said arresting position, and

means operable by said cyclically operable means for returning said pawl device to said retracted position independently of said spring. 

1. In a data printer having a printing impression means, a type member having teeth thereon, a plurality of type characters carried by said member, cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means, a stop pawl device having a part engageable with said teeth to arrest said member, means for guiding said pawl device from a retracted position to an arresting position for arresting said type member in different positions to present different ones of said type characters to said impression means, and means for moving said pawl device from said retracted position to said arresting position the combination with said pawl device of a snap-over spring engageable with said pawl device, means supporting said spring to yieldably maintain said pawl device either in said retracted position or in said arresting position, and means operable by said cyclically operable means for returning said pawl device to said retracted position and for maintaining said pawl device in said retracted position independently of said spring when said cyclically operable means is in said full cycle position.
 2. The combination according to claim 1 comprising means for pivotally supporting said pawl device for movement between said arresting position and said retracted position, the angle between said retracted position and an intermediate position representing the cross-over point of said snap-over spring being less that the angle between said arresting position and said intermediate position whereby said snap-over spring effects a greater detenting force against said pawl in said arresting position than in said retracted position.
 3. The combination according tO claim 1 comprising means for pivotally supporting said type member for movement about a first axis, means for pivotally supporting said pawl device for movement about a second axis, the engaging surfaces of each of said teeth and said device upon engagement extending perpendicular to a line passing between said axes whereby said surfaces will tend to drive said pawl device toward said member upon engagement of said surfaces.
 4. The combination according to claim 1 comprising means operable by said cyclically operable means for returning said member to said initial position, said teeth being effective during return of said type member from a position in which said member is arrested by said pawl device to move said pawl device from said arresting position to said retracted position.
 5. The combination according to claim 1 comprising means operable by said cyclically operable means for returning said member to said initial position, and means comprising said member when in said initial position for holding said pawl device in said retracted position.
 6. The combination according to claim 5 wherein said last mentioned means comprises an abutment on said member engageable with said pawl.
 7. In a data printer having printing impression means, a plurality of type members arranged side-by-side, a plurality of type characters carried by said members, means for yieldably advancing said type members to carry said type characters past said impression means, stop pawls engageable with said type members whereby to arrest said members, and means for guiding said pawls from retracted positions to arresting positions for arresting respective ones of said type members in different positions to present different ones of said type characters to said impression means the combination with said pawls of electromagnetic modules arranged side-by-side, each of said modules comprising a frame having first and second open guide cavities therein communicating with each other, an electromagnet carried by said frame, an interponent moveable in said first cavity and engageable with a said pawl, an armature moveable in said second cavity and engageable with said interponent, said armature being operable by said electromagnet to move said interponent to move said pawl from said retracted position to said arresting position, and the frame of each of said modules except a end one closing the said cavities in a neighboring one of said frames.
 8. The combination according to claim 7 comprising a third cavity in each of said frames for receiving a respective one of said electromagnets, the frame of the neighboring said module closing said third cavity.
 9. The combination according to claim 7 wherein the centers of said first cavities are located in a common plane, and alternate ones of said electromagnets are located on opposite sides of said common plane.
 10. The combination according to claim 7 wherein certain of the walls of said cavities guide the respective ones of said interponents and said armatures.
 11. The combination according to claim 1 wherein said last mentioned means exerts a greater force against said pawl device than said spring.
 12. In a data printer having a printing impression means, a type member having teeth thereon, a plurality of type characters carried by said member, cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means, a stop pawl device having a part engageable with said teeth to arrest said member, means for guiding said pawl device from a retracted position to an arrestin position for arresting said type member in different positions to present different ones of said type characters to said impression means, and means for moving said pawl device from said retracted position to said arresting position, the combinatIon with said pawl device of spring means for yieldably maintaining said pawl device either in said retracted position or in said arresting position, and means operable by said cyclically operable means for returning said pawl device to said retracted position and for maintaining said pawl device in said retracted position independently of said spring means when said cyclically operable means is in said full cycle position.
 13. In a data printer having a printing impression means, a type member having teeth thereon, a plurality of type characters carried by said member, cyclically operable means for yieldably advancing said member from an initial position to carry said type characters sequentially past said impression means, a stop pawl device having a part engageable with said teeth to arrest said member, means for guiding said pawl device from a retracted position to an arresting position for arresting said type member in different positions to present different ones of said type characters to said impression means, and means for moving said pawl device from said retracted position to said arresting position, the combination with said pawl device of a snap-over spring engageable with said pawl device, means supporting said spring to yieldably maintain said pawl device either in said retracted position or in said arresting position, and means operable by said cyclically operable means for returning said pawl device to said retracted position independently of said spring. 